In automotive radio systems, stereo speakers are normally mounted on the rear package shelf. The term, "package shelf," refers to that generally flat space immediately in front of the back glass and to the rear of the back seat. In large size cars, this shelf is fairly wide. It can be easily as wide as two feet in some models. In some models, it is relatively narrow, even in the range of only 4.0 or 5.0 inches. With smaller size vehicles, the package shelf is made more narrow, and this width is sacrificed to reduce the size of the car.
The width of the package shelf is a limiting factor on the size of the speakers which are mounted on it. Typically, speakers have been mounted heretofore by cutting a hole in the package shelf and bolting the speaker in the hole. A popular size of automotive speakers is 6.0 inches by 9.0 inches, and this size typically requires a package shelf about 7.0 or 8.0 inches in width to accommodate the 6.0-inch dimension.
Speaker performance is dependent in part on the dimensions of the speaker. A woofer gives good performance, but it ordinarily requires a relatively large diameter speaker cone. The optimum woofer is round and 10.0 inches or larger in diameter. A 6.0"-by-9.0" woofer provides passable sound. The 6.0"-by-9.0" is probably the limit in speaker performance insofar as directly mounted speakers are concerned. A longer, thinner speaker, perhaps 4.0 inches by 10.0 inches, can be installed, but it no longer really functions as a woofer because the narrow dimension of the oval limits the speaker cone and makes it perform more as a high frequency speaker, not a low frequency speaker. Thus, while it is possible to fabricate a speaker that is quite narrow in one dimension, it is not desirable from a performance point of view.
The present invention enables a high performance speaker system to be installed in an automobile, even though the automobile has a very narrow package shelf. Moreover, it permits installation of more than one speaker, namely, a large woofer and a small tweeter. Indeed, a third speaker, typically known as a mid range speaker, can also be installed if it is coaxially mounted above the woofer. The structure of this apparatus includes a speaker enclosure which is constructed of a hollow housing shaped at one end to form a circle to enable it to be mounted to a woofer of substantial size, such as a 10.0-inch or larger woofer speaker. The optimum woofer is circular, and, accordingly, this end of the enclosure is circular. The woofer is equipped with a stiff ring around the maximum diameter thereof, and the enclosure housing connects to the ring. The opposite end of the enclosure is constructed in the form of an oval. It has a surrounding shoulder for connection to the package shelf, and the oval opening has a minor dimension and major dimension which enable an elongate, oval opening to be cut in the package shelf. The width of the opening is determined by the maximum width permitted on the package shelf, while the length of the opening approximates the diameter of the woofer. The speaker enclosure, itself, is a hollow enclosure of rigid reflective material substantially free of internal obstructions which flares along its length in transition between the two end shapes specified. At the oval end, it also has room to support a relatively small tweeter centrally axially mounted in the oval opening.